Reduction of isothiocyanates

O-Prolected sugar thioformamides have also been prepared in 44-87% yields by tri-n-butyltin hydride reduction of isothiocyanate precursors in ether.156 For the preparation of 5-A-thioacylneuraminic acids (84), a chemoenzymatic route based on the M-acetylneuraminate pyruvate lyase-mediated condensation of the corresponding A -thioacyl-n-mannosamine derivatives (83) and sodium pyruvate has been reported.189 The enzyme-catalyzed aldol reaction was performed at pH 6.8 and afforded the desired compound in 55% yields (Scheme 24). 

AletalHydrides. Metal hydrides can sometimes be used to prepare amines by reduction of various functional groups, but they are seldom the preferred method. Most metal hydrides do not reduce nitro compounds at all (64), although aUphatic nitro compounds can be reduced to amines with lithium aluminum hydride. When aromatic amines are reduced with this reagent, a2o compounds are produced. Nitriles, on the other hand, can be reduced to amines with lithium aluminum hydride or sodium borohydride under certain conditions. Other functional groups which can be reduced to amines using metal hydrides include amides, oximes, isocyanates, isothiocyanates, and a2ides (64). 

Isocyanates and isothiocyanates are reduced to methylamines on treatment with LiAlH4. Lithium aluminium hydride does not usually reduce azo compounds (indeed these are the products from LiAlH4 reduction of nitro compounds, 19-59), but these can be reduced to hydrazo compounds by catalytic hydrogenation or with... 

Oxidative cleavage of amines 9-39 Reduction of amides 9-47 Reduction of nitro compounds 9-50 Reduction of nitroso compounds or hydroxylamincs 9-51 Reduction of oximes 9-52 Reduction of azides 9-53 Reduction of isocyanates, isothiocyanates, or N-nitroso compounds 9-55 Reduction of amine oxides 9-59 Reduction of azo, azoxy, or hydrazo compounds... 

Treatment of diarylphthalins, obtained by reduction of diarylphthalides, with sulfuric acid results in rearrangement to yield a mixture of benzo[c]furans and anthrones (34JA1406). When diarylphthalins (441) were reacted with sulfuric acid the benzo[c]furans (442) were isolated. A dimeric benzo[c]furan (443) was obtained when the phthalin (444) was treated with acetic anhydride or phenyl isothiocyanate. 

The presence of a thiocyanate group can be very easily deduced from the IR spectrum, which contains a sharp, but weaker in intensity, IR band around 2150 cm-1 and an NMR carbon resonance between 112 and 115 ppm. In the case of psamaplin B (172), C-NMR additivity effects applied to the methylene carbon linked to the thiocyanate were used to distinguish between a thio- and isothiocyanate group [142]. Chemical proof can be provided by LAH reduction of the thiocyanate, which gives a thiol rather than a methylamine group as the reaction product of the reduction of the isothiocyanate [195]. 

Microwave-induced imine formation, subsequent reduction with NaBH(OAc)3 and cyclisation of the resulting amino acid with isothiocyanates was used in an efficient one-pot multi-step synthesis of thiohydantoins (Scheme 4.26). The reductive animation was conducted as a two-step procedure to avoid direct reduction of the aldehyde at high temperatures48. 

Tetrakis(isothiocyanato)bis(2,2 -bipyridine)niobium(IV) is a medium-brown crystalline solid. It is only very slightly soluble in 1,2-dichloroethane, dichlo-romethane, and acetonitrile. These extremely dilute solutions of the complex readily decompose in the presence of oxygen or moisture however, in the solid state the complex appears to be air-stable. It does not melt or decompose below ca. 275°. The infrared spectrum, ultraviolet spectrum, magnetic moment, and x-ray powder diffraction pattern of the product obtained by this procedure are essentially identical to those obtained for the product prepared by the reduction of the hexakis(isothiocyanate)niobate(V) complex. ... 

The earliest method of this type, developed by Marckwald, employed the reaction of a-aminocarbonyl compounds (or their acetals) with cyanates, thiocyanates or isothiocyanates to give 3//-imidazoline-2-thiones. These compounds can be converted readily into imidazoles by oxidation or dehydrogenation. The major limitations of this synthetic procedure are the difficulty of synthesis of a wide variety of the a-aminocarbonyl compounds, and the limited range of 2-substituents which are introduced. The reduction of a-amino acids with aluminum amalgam provides one source of starting materials. The method has been applied to the preparation of 4,5-trimethyleneimidazole (83) from 2-bromocyclopentanone (70AHC(12)103), and to the synthesis of pilocarpine (84 Scheme 47) (80AHC(27)24l). If esters of a-amino acids react with cyanates or thiocyanates, the products are hydantoins and 2-thiohydantoins, respectively. 

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